Inductive position switching device

ABSTRACT

The present invention relates to a switching device, in particular a position switching device, which is intended to generate switching signals. The position switching device according to the invention comprises at least one switching unit and at least one activation unit, the switching unit reacting to a relative spacial displacement of the switching unit and the activation unit with respect to one another by outputting appropriate switching signals, characterized in that the switching unit is embodied as an inductive sensor unit and the activation unit is embodied as an inductive damping unit. The position switching device according to the invention is preferably applied in gear-speed-changing units for automatic gearboxes.

[0001] The present invention relates to a switching device, inparticular a position switching device, which is intended to generateswitching signals.

[0002] Different switching devices are known from the prior art, mostswitching devices using mechanical switches. However, a significantdisadvantage of these switching devices is that they have mechanicalswitching units or mechanical microswitches and mechanical slidingcontacts for generating switching signals. The mechanical switches havethe disadvantage that they do not operate without wear. Their servicelife is limited, on the one hand, by material erosion of contacts, bychanges in material (oxidation) and by deposition on the switchingcontacts which are caused by mechanical friction, electrical overloadingor the occurrence of an arc during the switching-off or switching-overprocess. The vibrations of the entire gate-type-gear changing unit alsolead to increased wear of of the sliding contacts and sliding tracks ofthe mechanical sliding switches.

[0003] Other switching units which eliminate the disadvantageousproperty of the mechanical switching contacts are known from the priorart. An example of such a wear-free switching contact is an inductiveswitching contact. Such an inductive switching contact is described inthe patent application “position sensor” with the official number EP 00101 661.7 submitted to the European Patent Office on Feb. 1, 2000. Theaforesaid European Patent Application has the same applicant as thisapplication.

[0004] The object of the present invention is to provide a switchingdevice or a position switching device which overcomes the aforesaiddisadvantage of the wear occurring with mechanical switch elements of aconventional mechanical switching device by using wear-free switchingunits. A further advantage of the present invention is to provide aposition switching device which permits reliable monitoring of theoperational capability of the position switching device and/or reliablesensing of a selected switched position.

[0005] This object is achieved using a position switching device whichhas the features of Patent claim 1.

[0006] The position switching device according to the inventioncomprises at least one sensor unit and at least one activation unit, thesensor unit reacting to a relative spacial displacement of the sensorunit and of the activation unit with respect to one another byoutputting switching signals (corresponding to the relativedisplacement). The difference between the position switching deviceaccording to the invention and other position switching devices knownfrom the prior art is that the sensor unit has been embodied as aninductive sensor unit and the activation unit has been embodied as aninductive damping unit.

[0007] A particular advantage of the present invention is obtained usinga position switching device in which either one activation unitsimultaneously activates two or more sensor units or the positionswitching device has at least two activation units and at least threesensor units, at least two of the activation units simultaneouslyactivating at least two of the sensor units.

[0008] The method of operation of the position switching devicesaccording to the invention can be clarified by means of the example inthe following figures.

[0009]FIG. 1 is a general schematic view of a preferred embodiment ofthe position switching device according to the invention,

[0010]FIG. 2 is a functional block diagram of a preferred embodiment ofan inductive sensor unit,

[0011]FIG. 3 is a schematic view of the method of operation of theinductive sensor unit,

[0012]FIG. 4 is an example of a switching criterion of the inductivesensor unit,

[0013]FIG. 5 is a possible embodiment of the inductive sensor unit,

[0014]FIG. 6 shows an application example of the position switchingdevice according to the invention,

[0015]FIG. 7 shows amplitudes of the sensor signals for gear-changingoperations of an automatic selector lever (represented in FIG. 6) fromposition 1 to position 4.

[0016]FIG. 8 is a schematic view of a further embodiment of the positionswitching device according to the invention.

[0017]FIG. 1 is a general schematic view of a preferred embodiment ofthe position switching device 1 according to the invention in the formof a gear-speed-changing unit for generating gear-speed-changing signalsfor an automatic gearbox. The position switching device 1 has switchingunits 2 and at least one activation unit 3, the activation unit 3 beingdisplaceable with respect to the switching units 2. The relativedisplacement of the switching units 2 and of the activation unit 3 withrespect to one another takes place both in the horizontal and verticaldirections. Displacement movements are thus understood both to be a puredisplacement movement and a tilting movement. The switching units 2 areembodied as inductive sensor units and the activation unit 3 is embodiedas an inductive damping unit whose method of operation is clarifiedusing FIGS. 2 and 3.

[0018]FIG. 2 shows a preferred embodiment of one of the inductive sensorunits 2. The inductive sensor unit 2 is composed of an oscillating powersource (Q˜) 11, an exciter loop (E) 12, a sensor loop (S) 13, a voltageamplifier (V) 14, an amplitude detector (D) 15 and an evaluation unit(A) 16. All or some of the components 11 to 16 of the inductive sensorunit 2 may be arranged on a printed circuit board 6 in a planar fashion.The exciter loop 12 is surrounded here by the sensor loop 13, or viceversa. Exciters 12 such as the sensor loop 13 can also be embodied withseveral windings.

[0019] The inductive sensor unit 2 functions as follows: the oscillatingpower source (Q˜) 11 impresses into the exciter loop 12 an electriccurrent which has changed over time. Said electric current generates amagnetic field M₁ which has changed over time and which has the fieldstrength H₁(x,y,z). The magnetic flux which has changed over time andwhich acts on the sensor coil 13 brings about a voltage in the sensorcoil 13, as in any electrical conductor, which is placed in the vicinityof the exciter coil 12. The sensor voltage is amplified by the amplifier14, the amplitude is determined with the detector 15 and the evaluationunit 16 compares it with a switching criterion K. FIG. 4 shows anexample of the switching criterion K. In simple switches, the evaluationcan be carried out by means of a comparator or a Schmitt trigger. Theevaluation unit 16 for multiple switches is usually in the form of amicrocontroller which passes on the switching information to the controlelectronics or power electronics via an interface (CAN, LIN, etc.).

[0020]FIG. 3 is a schematic view of the method of operation of theinductive sensor unit 2. If a conductive layer, plate or loop is placed,as an activation unit (B) 17 in the vicinity of the exciter coil 12, themagnetic field H₁ also penetrates this activation unit 3 and, accordingto Lenz, induces a voltage which brings about an eddy current I_(ks)which flows in the opposite direction to the current in the excitercoil. This short-circuit current which is also changed over timegenerates a magnetic field M₂ which acts in opposition to M₁, and, whenthe fields are superimposed on one another, this has an effect rangingfrom reducing to even extinguishing the entire magnetic field whichpenetrates the sensor coil 13. This leads to a reduction in the sensorvoltage and thus in the amplitude. This is compared with the switchingcriterion K by the evaluation unit 16 and triggers a switching function.The reduction in the sensor voltage by the actuator B can also bereferred to as damping.

[0021] The damping of the sensor signal is dependent on the distance (x)18 of the activation unit 3, embodied as an inductive damping unit, fromthe sensor loop 13: where x=0 the sensor signal is damped to a maximumdegree. The inductive damping unit 5 can be constructed from materialswith different degrees of electrical conductivity, for example frommetal, from a conductive plastic etc. The damping is also dependent onthe degree of overlap between the sensor loop 13 and the activationelement 3 or the inductive damping unit 5. If the inductive damping unit5 overlaps the entire area of the outer loop 13, the degree of coverageis 100% and the amplitude of the sensor signal is minimal. Two switchingsystems are therefore possible for the switch:

[0022] The degree of coverage G is kept to a defined magnitude and thedistance (x) between the activation element 3 and sensor loop 13 varies

[0023] or the distance (x) 18 is kept constant and the degree of overlapG is changed,

[0024] a combination of both is of course possible.

[0025] The inductive sensor unit 2 can also be extended to such anextent that one exciter coil 12 surrounds a plurality of sensor coils 13which are then connected to the amplifier via an analogue multiplexerAMUX. It is also conceivable to connect a plurality of exciter coils tothe power source Q in a series connection, which exciter coils surroundone or more sensor coils, such as is shown, for example in FIG. 5.

[0026] It is also conceivable to provide two activation units 3 andsensor coils 13 per switching position in order to provide a higherdegree of redundancy by means of a plausibility interrogation. In such acase, both switching signals must be identical at all times.

[0027] In addition it is possible to change the evaluation unit 16 insuch a way that it does not trigger a switching function by comparisonof the sensor voltage with a threshold value but rather triggers itadditionally by comparison with the voltage of an adjacent sensor.

[0028] With the inductive sensor unit 2 it is also possible to constructa pressure switch as follows. The activation unit 3 is mounted on aplunger which can alternately be locked in two positions similarly to aballpoint pen mechanism. It is also conceivable to configure themechanics of the pressure switch in such a way that the plunger does nothave latching positions but can instead be displaced “freely” withrespect to the sensor unit or the sensor sliding plane. If the distancebetween the activation unit 3 and sensor sliding plane is, for example,5 mm in the (latched) position P1 and 0.5 mm in the (latched) positionP2, a standardized amplitude voltage of approximately 0.5 must be setfor the switching criterion K for the switching range shown in FIG. 3.However, a pressure switch can also be embodied in such a way that amechanism changes the degree of coverage G of the activator with respectto the sensor loop 13. The sensor amplitude voltage then depends on thedegree G of coverage and must be defined according to its characteristiccurve.

[0029] If a plurality of positions are to be detected, it is expedientto combine a plurality of switching units 2 as a functional unit. Agear-speed-changing device 20 for an automatic gearbox is illustrated inFIG. 6 as an example of the use of a position switching device 1according to the invention. FIG. 6 shows by way of example what isreferred to as a gate-type-gear changing unit such as is known generallyas the prior art from the user's point of view. However, the use ofinductive switches in conjunction with a gate-type-gear changing deviceis novel. These inductive switch designs are particularly expedient fora logic control, that is to say for a case in which the gear speeds inan automatic gearbox are not selected in a directly mechanical way.

[0030] A printed circuit board 6—as illustrated in FIG. 1—is positionedunder the panel or cover 21 and, for example, the back lighting of thepanel displays (“1”, “2” . . . , “P”) can be mounted on its upper side.An activator carriage (BS) 24, which rests in a planar fashion on theunderside of the printed circuit board LP 6 is connected to the gearlever or automatic gear selector lever (AW) 22, which dips through anopening 23 in the printed circuit board, one or more activation units 3,for example two activation units BF1 and BF2 here, which can bedisplaced at a defined distance by means of the different inductivesensor units (SE*) 2 being provided on said activator carriage (BS) 24.The switching unit SE5 which is represented in FIG. 1 can be used toregister a further switched position of the gear selector lever 22. Thisswitched position does not, however, occur in gear-speed-changingdevices which are generally known from the prior art. For example thegear-speed-changing device 20 which is represented in FIG. 6 does nothave any gear speed selector lever switched position corresponding tothe sensor unit SE5. This embodiment of the gear-speed-changing deviceis thus optional, i.e. the sensor unit SE5 can be omitted.

[0031] When a plurality of inductive switches are combined, the blockcircuit diagram as illustrated in FIG. 5 is obtained. A current source11 supplies the exciter coils 12 of a plurality of sensor units (SE*) 4.The signals of the sensor loops 13 of a plurality of sensor units 2 areconnected to the amplifier 14 via a wear-free semiconductor switch(AMUX). The specification of which sensor unit is to be connected isreceived by AMUX from the evaluation unit 16 via the addressspecification AV. The evaluation unit 16 outputs the switched state as afunction of the address specification. The associated sensor signal isdamped as a function of the degree of overlap between the activator areaof the activation unit 3 and the sensor unit (SE*) 4. If the switchingthreshold SW of the signal which can be set at the evaluation unit 16 isreached, the position of the switch is detected as a valid position andswitched over.

[0032] An alternative to the previously proposed signal evaluation meanswith static threshold value comparison is to compare the sensor signalsfrom two adjacent sensor units 2. If the signal of a sensor unit 2 islower than that of the adjacent sensor unit 2—in which case a hysteresiscan also be taken into account, as illustrated in FIG. 7—it is to beassumed that there is to be switching over from one position to theother. This results in switching thresholds being defined in a way whichis very resistant to external influences such as temperature drifting ofthe amplifier 14, of the power source 11 etc.

[0033] It is also possible to carry out extremely redundant positiondetection without a large degree of additional expenditure using theposition switching device 1 according to the invention. It is proposedto install at least two sensor units 2, instead of one sensor unit 2 perswitched position, and to continue to compare the signals. Givencontradictory results, the evaluation unit 16 should carry out theswitching function in such a way that the entire system is placed in thesafe state. For this purpose, the printed circuit board 6 can beequipped, for example, with safety sensor units (SSE*) 2, as isillustrated schematically in FIG. 8. Here too, the sensor unit SE5 andthe corresponding safety sensor unit SSE5 can be used to registerfurther positions of the gear selector lever 22. For agear-speed-changing device 20 represented in FIG. 6 it is possible toomit such a switched position.

[0034] A further embodiment of the position switching device 1 accordingto the invention is obtained if, instead of pairs composed of one sensorunit (SE*) 2 and one safety sensor unit (SSE*) 2, as is illustrated inFIG. 8, just one sensor unit 2 is used; for example instead of SSEP andSEP, only SSEP; instead of SSER and SER only SER; instead of SSEN andSEN only SSEN etc. In this case, the sensor units 2 are accommodatedrelatively far apart from one another on the printed circuit board 6.This structure of the position switching device 1 makes it possible toavoid the undesired secondary damping effects which are caused bydisplacements of the activation units 3.

1. Position switching device (1) comprising at least one switching unit(2) and at least one activation unit (3), the switching unit (2)reacting to a relative spacial displacement of the switching unit (2)and of the activation unit (3) with respect to one another by outputtingappropriate switching signals, characterized in that the switching unit(2) is embodied as an inductive sensor unit and the activation unit (3)is embodied as an inductive damping unit.
 2. Position switching unit (1)according to claim 1, characterized in that at least two switching units(2) are positioned on a common carrier unit (6) and/or are integratedinto a common carrier unit (6).
 3. Position switching device (1)according to claim 2, characterized in that the carrier unit (6) is aprinted circuit board (7).
 4. Position switching device (1) according toone of the abovementioned claims, characterized in that the activationunit (3) can be displaced horizontally and/or vertically with respect tothe switching unit (2).
 5. Position switching device (1) according toone of the abovementioned claims, characterized in that the activationunit (3) is connected to an activation element (8) which can bedisplaced with respect to one or more switching units (2), a specificposition of the activation element (8) with respect to the positionswitching device (1) corresponding to a specific position of theactivation unit (3) with respect to the switching unit (2) or theplurality of switching units (2).
 6. Position switching device (1)according to one of the abovementioned claims, characterized in that anactivation unit (3) activates just one switching unit (2) at a giventime.
 7. Position switching device (1) according to one of claims 1 to5, characterized in that an activation unit (3) activates two or moreswitching units (2) at a given time.
 8. Position switching device (1)according to one of the abovementioned claims, characterized in that theposition switching device (1) has at least two activation units (3). 9.Position switching device (1) according to one of claims 7 and 8,characterized in that the position switching device (1) outputsredundant switching signals.
 10. Position switching device (1) accordingto claim 9, characterized in that the redundancy of the switchingsignals is used to monitor the operational capability of the positionswitching device (1).
 11. Gear-speed-changing unit (20) for generatinggear-speed-changing signals for an automatic gearbox, characterized inthat it uses the position switching device (1) according to one of thepreceding claims for generating gear-speed-changing signals. 12.Gear-speed-changing unit (20) according to claim 11, characterized inthat it is embodied in the form of a gate-type-gear changing unit.